1. Field of the Invention
The present invention generally relates to apparatus and methods for performing surgical, transcatheter or minimally invasive repair of a defective cardiac valve, such as the mitral, aortic, tricuspid and pulmonary valves.
2. Description of the Prior Art
The human heart has four major valves which moderate and direct blood flow in the cardiovascular system. These valves assure a unidirectional flow of blood supply through the cardiovascular system. Whereas the aortic, pulmonary, and tricuspid valves have three leaflets, the mitral valve has only two leaflets. The mitral valve and aortic valve control the unidirectional flow of oxygen-rich blood from the lungs to the body. The mitral and aortic valves direct the oxygen-rich blood received from the lungs into the systemic circulation under the pumping action of the left ventricle. The tricuspid and pulmonary valves ensure unidirectional flow of oxygen-depleted blood received from the right atrium towards the lungs by the pumping action of the right ventricle.
Heart valves are passive structures composed of leaflets that open and close in response to differential pressures on either side of the valve. As an example, oxygen-rich blood flows from the lungs into the left atrium. When the left ventricle expands, the low pressure under the mitral valve allows it to open for blood flow from the left atrium to the left ventricle. When the ventricle contracts to pump blood out to the body, a high pressure is created under the mitral valve, closing it to prevent blood from leaking back toward the atrium into the lungs.
Congenital, inflammatory, infectious conditions or diseases may lead to dysfunction of the valves over time. Such degradation may result in serious cardiovascular compromise or even death. The mitral valve and the aortic valve which are subjected to the systemic circulation high pressure generated by the left ventricle are more susceptible to dysfunction, such as stenosis or regurgitation.
For example, a stenotic mitral valve may impede blood flow into the heart, causing blood to back up and pressure to build in the lungs. Regurgitation occurs when the mitral valve leaflets do not coapt correctly, thus causing blood to leak backwards into the left atrium and lungs each time the heart pumps. Improper coaptation of the mitral valve leaflets thus requires the heart to pump more blood with each contraction to eject the necessary amount of blood for systemic circulation; a process called volume overload. Although the heart may gradually compensate for this overload as the leakage progresses slowly through months and years, the heart will eventually begin to fail.
Medical treatments to address dysfunctional valves involve either repairing the diseased native valve or replacing it with mechanical or biological valve prosthesis. All current valve prostheses have disadvantages, such as need for long-term maintenance with blood thinners, the risk of clot formation, limited durability, etc. Valve repair, due to its short term use of blood thinner and low risk of thrombosis, is preferable to valve replacement when possible. Today, standard valve replacement or repair procedure still requires an open-heart surgery which is prone to many complications and long hospital stays for recuperation.
Percutaneous techniques have been developed recently for less invasive implantation of a replacement valve without the need for open-heart surgery. In such techniques, the replacement valve is crimped to a small profile compatible to the blood vessel lumen size, and then mounted to the end of a flexible catheter. It is then advanced through the blood vessel of a patient until the prosthetic valve reaches the implantation site. The valve is then deployed to its functional size at the site of the defective native valve. The expansion of the valve to its normal size could be through self-expansion or by balloon expansion. The expanded prosthetic valve pushes the native valve leaflets aside and renders them ineffective. Examples of such devices and techniques, wherein the native valve is replaced in its entirety by a substitute tissue valve, are described, for example, in U.S. Pat. Nos. 6,582,462 and 6,168,614 to Andersen et al.
With the success of percutaneous valve replacement in the aortic position, catheter-based mitral valve replacement and repair techniques for correcting mitral regurgitation have been pursued. Several technologies have been developed ranging from iterations of the Alfieri stitch procedure, to coronary sinus-based modifications of mitral anatomy, to subvalvular placations, or ventricular remodeling devices.
Mitral valve regurgitation often arises due to mitral annulus dilatation, which may be treated using a surgical technique to narrow and restore the natural shape the annulus. Prosthetic annuloplasty rings are therefore an important addition to mitral valve repair techniques. A primary role of the annuloplasty ring is to reduce the size of the annulus and decrease the tension on the sutures while providing flexibility and mobility at the same time.
One recent technique for correcting mitral valve leakage is described in U.S. Pat. No. 6,269,819 to Oz et al., which employs a percutaneously introduced clipping apparatus into a leaking mitral valve. Once positioned, the clip arms are activated to hold a short segment of the coaptation edges of both the anterior and posterior leaflets together to reduce mitral regurgitation. Because the clip transforms the mitral orifice into two orifices, the clip may significantly obstruct the flow of blood through the valve.
The native structures of the mitral valve apparatus (mitral annulus and leaflets, chordae, papillary muscles, etc.) play an important role in left-ventricular function and therefore any valve replacement system that does not respect these elements may adversely impact the left-ventricular function. Current trans-catheter mitral valve replacement in development requires anchoring the device to the annulus and leaflets of the native valve. This immobilizes the native leaflets, exerts tension to the chordae, and impairs the native function of the annulus, which can result in left-ventricular outflow tract (LVOT) obstruction and systolic anterior motion (SAM), etc.
In view of the above-noted drawbacks of previously-known systems, it would be desirable to provide a device, and methods of using the same, that assists the functioning of the native cardiac valve, rather than removing or entirely supplanting the native valve. It would also be desirable to provide a device having prosthetic leaflets, and methods of using the same, that reduce tension on the prosthetic leaflets, thereby increasing the life of the prosthesis. It would be further desirable to provide a device having a support frame, and methods of using the same, wherein the prosthesis is configured to self-align with the native valve annulus when deployed, without deformation. It would also be desirable to provide a device, and methods of using the same, that may be deployed with reduced risk of obstructing blood flow relative to previously known mitral valve repair techniques.